Scanning electron microscopic imaging of surface effects in desorption and nano‐desorption electrospray ionization

Abstract

Scanning electron microscopy was used to investigate rivulets that are formed on the analyzed surface during desorption electrospray ionization (DESI) experiment. Ferromagnetic nanoparticles added to the spray solvent in a form of colloid solution functioned as an additional surface probe. The existence of the rivulets was confirmed on glass and newly demonstrated on two different types of porous polytetrafluoroethylene (PTFE). The results show that in standard DESI set-up the rivulets are arranged into very regular shapes. Same rivulets were obtained in DESI experiments without high voltage on the sprayer. However, no such rivulets or any other regular patterns were found on a surface in nano-DESI (nanospray DESI without the carrier nebulizing gas) experiments. This indicates that symmetrical rivulets are created by the hydrodynamical rather than electrostatic forces. It was also demonstrated that blocking the rivulets by a simple physical barrier did not influence known surface charging effects.

Lateral resolution of desorption nanoelectrospray: a nanospray tip without nebulizing gas as a source of primary charged droplets

“…Previously, nanoDESI has always been used with ion trap mass spectrometers. [11][12][13][14][15] To acquire more experimental points per second, nanoDESI was newly coupled to a Q-TOF mass spectrometer. Its higher resolving power and accurate mass measurement might also improve the selectivity and identification capability if needed.…”

“…13 A smaller surface area is affected by nanoDESI in comparison with standard DESI. 14 The internal energy of formed ions and salt tolerance of nano-DESI have been recently described 15 but its potential in mass spectrometry imaging has not yet been evaluated.…”

Role of Electrochemistry in Desorption Ionization Mass Spectrometry (LS DESI MS) of Aqueous Samples Containing Electrolyte Salts

“…The LS interface during operation of angled LS DESI MS system is shown in Figure C. Here, when the ESSI -generated spray came in contact with the LS at the horizontal cross section of the LS capillary, several small streams (rivulets) , were observed, which flowed toward the capillary edge, forming a liquid cone at the edge. A secondary spray emerged from the cone, as in in-line LS DESI MS (Figure C).…”

Effects of Tailored Surface Chemistry on Desorption Electrospray Ionization Mass Spectrometry: a Surface-Analytical Study by XPS and AFM

“…Several papers have been published on the ionization mechanisms leading to the formation of isolated gasphase ions, supporting the hypothesis of a two-step, dropletpick-up model followed by ESI-like desolvation and gas-phase ion formation by the action of the electric field [4][5][6][7]. In this context, the roles of surface and pneumatic effects on ionformation yield have recently been examined, by investigating surface charge [8,9], hydrodynamic and pneumatic forces [10][11][12][13], and interactions between analytes and the surface [14]. In the present study, surface-chemistry effects on DESI-MS response have been thoroughly investigated and correlated with the ion-formation yield.…”